Much of the liquid and gas utilized in the world, and particularly hydrocarbon liquids and gases, are transmitted from areas of production to areas of consumption through pipelines. To keep the interior of the pipelines clean, to separate different components, and to perform surveying functions, devices known as pipeline pigs are frequently used. Since the pipeline pigs may move at various speeds in the pipeline depending upon the velocity of fluid flow and other factors, it is sometimes difficult for the operator of a pipeline to know the location of a pipeline pig or to know when a pipeline pig has passed a certain point in a pipeline.
Various pig signals are known in the industry and are commonly available in the marketplace. These signals typically have a tubular body member or nipple which is mounted on the pipeline by welding or other means. The tubular body has a small diameter opening into the pipeline such that it is in fluid communication with the interior of the pipeline. A stem assembly is typically sealably placed inside the tubular body member thus sealing off the interior of the tubular body member and interior of the pipeline from the atmosphere. The stem has a shaft or trigger which extends into the interior of the pipeline. When the pipeline pig passes by the tubular body member it contacts the shaft. This contact then releases a spring loaded flag or other signal fixedly secured to the exterior of the tubular body member. This is accomplished through various mechanical and/or magnetic means.
Early pig signals used a mechanical linkage to release a spring loaded flag. More recent developments in this field have taken advantage of magnetic linkages to release a spring loaded flag. However no matter what type of mechanism was used to link the interior movement of the shaft to the releasing mechanism of the flag, the prior art flag assembly was always secured to the stem assembly and/or tubular body member by means which kept it in predetermined, fixed orientation relative to the stem assembly and/or tubular body member.
Because the flag is much easier to see from the front rather than a side view it is often beneficial to rotate the flag such that the flag faces the direction of an observer. Given the prior art design of the flag assembly being fixedly attached to the tubular body or stem assembly, the rotating of the flag requires either the tightening or loosening of the threadably engaged stem assembly. This could lead to the stem being either over tightened or too loose, or adjusted under pressure which may be a safety concern.
The other option was to unbolt the flag assembly from its mounting and re-bolt it in a different orientation. The drawback to the prior art in this situation is that the flag assembly can only be reoriented to a very limited number of orientations, typically 90 degree increments. Many times the optional orientations do not provide optimized viewing of the flag.
The external threads on the nipple often suffer from weathering and corrosion. The prior art generally does not address this problem.